I hate the rush that Mewtwo and CMT's T1 Tornadus puts on the game. I'm all for having fast decks, but being able to T1 KO for 80+ damage is too fast, especially with the current first turn rules. So much power in one turn puts too much emphasis on who goes first and whoever has the better hand. I'm not talking about a dead hand vs a playable hand, I'm talking one or two card differences in your first hand that can decide the game. Between having to go first and having the better hand, it feels like the luck factor is intensified. A little bit of luck is okay, but the format the way it is now leaves room for too much luck. JMO.
On topic: It still depends on your deck, like I've seen Typhlosion variants do fine with 1 Mewtwo while most other decks (excluding Terrakion and Durant) need 2. CMT can also do 3 to cover the mirror without worrying about prize issues. And of course there's just CM which can go to 3 or even 4.